1. Field of the Invention
The present invention relates to a VDT (video display terminal) stress mitigating device and method, a VDT stress risk quantifying device and method, and a recording medium for reducing VDT stress such as excessive strain and fatigue caused by visual irritation.
The present application is based on an application for a patent in Japan (Japanese Patent Application Laid-Open (JP-A) No. 11-333429) and the contents disclosed in the above Japanese patent application have been incorporated as a portion of the present specification by reference.
2. Description of the Related Art
Conventionally, image display devices exist, as typified by television receivers, for visually displaying information to people. Various physical symptoms caused by the use of these image display devices are known as what is termed “VDT (video display terminal) stress disease”. Hitherto commonly known types of VDT stress include a reduction in visual ability and eyestrain due to long hours of continuously looking at images displayed on an image display device. These types of stress are not connected to the content of the images themselves, but are mainly caused by the way in which the image display device is used.
In contrast, recent years have seen a diversification of graphic expression that has accompanied technological advances in computer graphics and the like. The risk of content generated VDT stress that is caused by the content of the graphics has been pointed out as a new mechanism of VDT stress. Graphic content that causes this type of VDT stress includes intraframe flicker, when a frame image in frequencies between approximately 10 Hz to 30 Hz contained in the graphic content flickers violently. There have been reports that, due to this type of content generated VDT stress, excessive strain and fatigue is caused in the cranial nervous system and the like, and that symptoms resembling travel sickness and, in some cases, even convulsions have been caused.
As a conventional technology for effectively preventing content generated VDT stress, there are known a method and device for selectively attenuating temporal frequency components in the neighborhood of 10 Hz where content generated VDT stress most commonly occurs, such as is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 07-101977 “VDT Stress Mitigating Method, Image Frequency Attenuating Device, and VDT Adapter”.
However, in contrast to the aforementioned intraframe flicker in which the frame image flickers depending on the graphic content, even if the graphic content does not involve a flicker phenomenon, as is the case with a static image, then, as can be seen, for example, in the finely striped pattern in the example shown in FIG. 14, the possibility has been pointed out that content generated VDT stress may be caused in people who are predisposed to be hypersensitive to light even when the graphic image is a regular spatial pattern in which the same shapes are arranged in a regular repetition within a space.
However, at present, there is no known technology for mitigating content generated VDT stress caused by this type of regular spatial pattern or for detecting the degree of risk of this type of VDT trouble.
Moreover, in the same way as with regular spatial patterns, even in static images that do not contain any flicker phenomenon in the graphic content itself, when a stripe pattern in the direction of the scan line (horizontal stripes) is displayed at an interval equivalent to the scan line interval on an image display device having an interlaced format, such as NTSC, PAL, or the like, then flicker having a temporal frequency of the frame frequency (30 Hz in NTSC, 25 Hz in PAL) is unexpectedly generated and, as a result, in some cases the same stress as content generated VDT stress is generated.
Specifically, in an interlaced format, because the two fields that form a single frame are scanned at a frequency twice the frame frequency and the two field images within the one frame are divided temporally and displayed in sequence, then, as is shown in FIG. 3 below, for example, when the graphic portions of the striped pattern (i.e. the black portion) and the background portions belong to separate fields, the graphic portions and the background portions are displayed alternately, and flicker having a temporal frequency of the frame frequency is generated.
According to the technology disclosed in the above JP-A 07-101977, it is possible to suppress intraframe flicker. However, because this technology performs a temporal filtering process on each pixel independently, it is not possible in principle to mitigate content generated VDT stress caused by regular spatial patterns contained in the graphics, or VDT stress caused by the aforementioned flicker generated when field images are displayed alternately in an interlaced format. Moreover, nor is it possible to quantatively detect the risk of this type of VDT stress.